A blender is used to mix, stir, liquefy and otherwise process foods and beverages. A typical blender has a motorised base with a removable jug, the jug being isolated from the outside environment by a lid. Vigorous blending within the jug can cause the lid to dislodge as a result of pressure changes within the jug. To resolve this problem in the past, blenders have employed interference fit seals and locking structures such as bayonet features to resist those forces which tend to dislodge the lid.
Other food processing devices have similar problems when pressure or forces from rotating blades or tools, heat, hot air or steam within a processing vessel act to dislodge the vessel's lid. The problem is exacerbated when the level of food within the vessel is high.
The present invention seeks to overcome the problem of inadvertent dislodgement of the lid by managing the airflow the food and liquid processing environment and by providing an outlet valve, check-valve or passageway that ensures that the lid will not become dislodged as a result of the movement air or foods within the jug or vessel. The invention has application to any food processing vessel having a lid and a rotating blade.